1. Field of the Invention
This invention reIates to a process for making a fabric that has specific barrier properties and to the product of that process. More particulary, the invention concerns such a process in which a lightweight continuous coating of polypropylene is applied to a fibrous base sheet and then calendered to produce a fabric that is permeable to vapor and impermeable to liquid.
2. Description of the Prior Art
Fabrics that are vapor-permeable and water-impermeable have long been sought for a wide variety of uses. Strong fabrics having such transmission and barrier characteristics would be particularly useful in building construction, for example as a roofing-tile underlayment (i.e., "underslatement") or as an air-infiltration barrier which reduces heat losses through walls, ceilings and around joints.
Many methods have been suggested for obtaining fabrics that are relatively water impermeable and vapor permeable. For example, woven or nonwoven fabrics have been coated with polymeric materials that are filled with substances which cause the polymeric material to form fissures, when the coated fabric is worked or heated or when the filler is dissolved from the structure. Also, various types of foamed coatings and coated poromeric structures have been suggested. However, when used as a roofing tile underlayment or as an air-infiltration barrier, the prior art materials have exhibited shortcomings in their combination of strength, barrier and transmission properties.
The object of the present invention is to provide a process for making a coated fabric that would be suitable for use as an air-infiltration barrier or as a roofing-tile underlayment The invention also comprehends the new fabric made thereby.